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Homework Help: Battery / circuit problem

  1. Feb 28, 2006 #1
    Here is my question: Is it possible to connect 2 identical batteries to make 2 bulbs connected in series light just as brightly as one bulb connected to one battery?

    Reasoning: lets say each battery has a voltage of 1.5V and that each light bulb is equal and has a resistance of 4 ohms.
    Now in circuit 1, with two identical batteries and bulbs, the current flowing through the circuit would I = (1.5V+1.5V) / (4ohms+4ohms) = .38 A
    Now in circuit 2, with one battery and bulb, the current flowing through the circuit would be I = (1.5V) / (4ohms) = .38A

    We know that the amount of current flowing through a light bulb determines its brightness, and thus in circuit 2, .38 A is flowing through 2 bulbs, and in circuit 1 the same amount of current is flowing through only 1 light bulb, thus it is not possible,

    Can someone tell me if this is right? Much appreciated.
  2. jcsd
  3. Feb 28, 2006 #2


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    Current is continuous through all parts of a series circuit. Consider two bulbs in series: if one bulb has 0.38 A flowing through it, the other must also.

    Consider electrons in a wire to behave much like water in a pipe. If some volume of water is flowing through part of a pipe every second, the same volume must be flowing through every other part of the pipe every second.

    In the case of (1 bulb, one battery), the bulb drops 1.5V and carries 0.38A of current. In the case of (2 bulbs, 2 batteries), each bulb drops 1.5V and carries 0.38A. Each of those two bulbs would be lit identically to the single bulb, single battery situation.

    - Warren
  4. Feb 28, 2006 #3
    I think it also depends on what the voltage drop across each bulb (resistor) is.
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